Core-Shell Compositional Fine Structures of Dealloyed PtxNi1-x Nanoparticles and Their Impact on Oxygen Reduction Catalysis

Using aberration-corrected scanning transmission electron microscopy and electron energy loss spectroscopy line profiles with Angstrom resolution, we uncover novel core-shell fine structures in a series of catalytically active dealloyed PtxNi1-x core-shell nanoparticles, showing the formation of unusual near-surface Ni-enriched inner shells. The radial location and the composition of the Ni-enriched inner shells were sensitively dependent on the initial alloy compositions. We further discuss how these self-organized Ni-enriched inner shells play a key role in maintaining surface lattice strain and thus control the surface catalytic activity for oxygen reduction.